Electronic power conversion apparatus



April 22, 1947.

A. SCHMIDT, JR ELECTRONIC POWER CONVERSION APPARATUS Inventor":

Filed June 12, 1944 August Schmidt, Jn,

Hi torneg Patented Apr. 22, 1947 UNITED STATES FATEN'BY OFFICEELEC'ERGNIC POWER GONVERSION APPARATUS August Schmidt, .lr., llislrayuna, N. assignor to General Electric Company, corporation of NewYork Application June 12, 1944, Serial No. 539,939

9 Claims. 1

My invention relates to electronic power conversion apparatus and morepar'cularly to electronic apparatus for converting alternating currentpower from one frequency to alternating current power of the same or ofa different frequency.

The electronic power conversion system of my present invention is of thetype known the art as a dual conversion system wherein alternatingcurrent of one frequency is rectified by electronic rectifying apparatustransmitted as direct current over a high voltage direct currenttransmitting circuit and then inverted by electronic means toalternating current of the same or of a different frequency. Suchapparatus may be used to interconnect two electrical systems, and may beclassified as a tie line, a frequency converter, or a direct currentpower transmission system, depending upon. the principal functionperformed by the apparatus.

In systems of this type requiring outputs in the thousands of kilowatts,it is found expedient, in View of the present current and voltage ratingof electronic tubes, to utilize a plurality of rectifiers inverterunits. Heretofore, the rectifier units have been connected in series,and likewise the inverter units, with. the direct current loopinterconnecting the two series connected groups of conversion apparatus.With this arrangement'the voltage level and insulation stresses of thesystem are greater than is desired, the flexibility in utilization ofthe various units is not adequate for man purposes, and reduction incommunication interference is not readily obtained.

It is, therefore, an object of my invention to provide a new andimproved arrangement for electronic power conversion apparatus.

It is another object of my invention to pro Vide a new and improvedarrangement for a plurality of electronic power rectifiers and invertersso as to reduce the voltage level and the insulation stress of thesystem appreciably below that experienced in the arrangements heretoforeproposed or used as referred to above.

It is a further object of my invention to provide a new and improvedarrangement of a p1urality of power rectifiers and inverters whichaffords flexibility in utilization of the severunits whereby separateand independent, operation of a portion of the units may he obtainedwell as joint operation of all units.

It is a still further object of my invention to provide a new andimproved arrangement in electric power conversion apparatus foreiiecting phase multiplication and thereby minimizing interference withcommunication circuits.

My invention will he better understood from the following descriptiontaken in connection with the accompanying drawing and its scope will bepointed out in the appended claims.

The single figure of the accompanying drawing is a diagrammaticrepresentation of one embodiment of my invention particularly arrangedfor a double-unit power conversion unit.

In the single "figure of the accompanying drawing, I have representedtwo alternating current power ystems i and 2 which, by way of example,will be assumed to be cycles and 25 cycles, respectively. With thisassumption the electronic conversion apparatus may be referred to as afrequency changer although it will be obvious to those Skilled in theart that my system is equally applicable to a high voltage, directcurrent transmission, a tie line, or various other conversion functions.For simplicity of identification the top unit, as viewed in the drawing,is designated as A and the bottom unit as B. Unit A is connected tothealternating current system 9 through two transformers 3 and 4.Transformer ii comprises a Y-connected primary windand a secondarywinding 6 which is zigzagged for a phase displacement of plus 7 /2electrical degrees. Transformer l comprises a delta connected primarwinding l and a secondary winding 8 similarly zigzagged for a phasedisplacement of plus 7 /2 electrical degrees. The primary windings 5 andl are connected in parallel and to th circuit i through a circuitinterrupting device s. Since double-way rectification, to be describedpresently, is used a 12 phase wave form is obtained hy using the twothree phase secondary windings displaced thirty electrical de Unit B issimilarly connected to the circuit 5 through transformers H and I2 whichare pro. ed with a delta connected primary wind and respectively,connected in parallel and the circuit l through the circuit interrupterTransformers l I and I2 are also provided with zigzagged secondarywindings Hi and ii, respectively. Each of these secondary ings iszigzagged for a phase displacement or minus I /3 electrical degrees.

Unit A is also connected to circuit 2 through tr nsformers it and iswhich are arranged similarly to transformers 3 and l for 12-phaseoperation and connected to circuit 2 through circuit interrupting meansas. Unit B is likewise connected to circuit 2 through transformers 2iand 22 arranged similarly to transformers H and i for lZ-phase operationand connected to circuit 2 through circuit interrupting means 23. Eachof the secondary windings of transformers l8 and i9 is zigzagged 7 /2plus while the secondary windings of transformers 2| and 22 arezigzagged 7% minus. Thus by connecting all of the transformer secondarywindings of unit A 7 /12 degrees plus, or leading, and the secondarywindings of unit B 7 /2 degrees minus, or lagging, an overall 24-phaserelationship is obtained when both units are being operated.

Sectionalizing switches 24 and 25 may be intel-posed in circuits l and2, respectively, between units A and B.

Each of the converter units A and B is shown as comprising four tubegroups which are similar in arrangement in the two units, and forpurposes of simplicity in explanation the detailed description will bedirected more particularly to the power portion, as viewed in thedrawing, of the unit B. The unit B comprises four tube groups 26, 2'1,28 and 29. Tube groups 25 and 2'! may be considered as rectifiers andtube groups 28 and 29 as inverters, or vice versa, depending upon theassumed direction of power flow. Each tube group comprises six tubesconnected in a three-phase double-way circuit as shown, for example, intube group 26, in which tubes 180 degrees apart in phase position aremounted back to back with the cathooe of the upper tube connected to theanode of the tube below it. This three-phase double-way circuit is adesirable arrangement because of its high apparatus economy and goodoperating characteristics. In accordance with my invention, the tuberoups 26, El, 28 and 29 are connected in an alternate arrangement suchthat, with the assumption that tube groups 26 and 2? are rectifiers andtube groups 28 and 29 are inverters, the direct current loop circuit 30may be traced from the lower direct current terminal of rectifier tubegroup 27 to the upper direct current terminal of inverter tube group 28,from the lower direct current terminal of inverter tube group 28 to theupper direct current terminal of rectifier tube group 26, from the lowerdirect current terminal of rectifier roup 26 to the upper direct currentterminal of inverter tube group 29, and from the lower direct currentterminal of inverter tube group 29 and back to the upper direct currentterminal of rectifier tube group 21; thus closing the direct currentloop through the tube groups. Briefly stated, the circuit proceeds fromrectifier 27 to inverter 28, to rectifier 26, to inverter 29 and back torectifier 2?. With this alternate arrangement of the tube groupsassociated with the respective alternating current circuits l and 2, thevoltage level in the direct current loop 36 is minimized because thecontiguous tube groups function oppositely at all times-one serving as arectifier to produce a unidirectional voltage and the other serving asan inverter to absorb the unidirectional voltage. In accordance with myinvention, the neutral terminal of a transformer secondary of eachconverter unit, such as the neutral terminal of transformer winding llof unit B and the neutral terminal of transformer secondary winding 8 ofunit A are grounded at points 3| and 32, resp t y the insulation stressof the transformer secondary windings and the direct current loop isfurther reduced. The alternate connection of rectifier tube groups andinverter tube groups and the grounding, as specified, results inreducing the insulation stress direct voltage of one tube ctiveoperation voltage is one tube group.

w A corresponding to ave been assigned the same a prime mark for ease ofsh c groups are connected in an alternate a1 out in tl' s9 6 manner ashas described in C(llllECBlOIl with such as a disconnect switch, a creactor and a current limiting rea r. I17135 the group 26 of unit isconnected to transformer secondary windll through a disconnect switch34, a commutating reactor and a current limiting reactor 35. In likemanner, the tube group 29 is connected to the secondary wi oi"transformer "'3 through disconnect switch 3 a comreactor and a currentlimiting re-- r group of unit B is connected ary winding 93 throu h adisconnect switch or reactor 4i and a current lii iting reactor w. Tubegroup 28 of unit B is connected to the secondary w nding of transformer2! through a snnect switch a mutating reactor '54 current limitingreactor 525. The commutati g reactors M and 44 and and 35 are eachrepresented by a rectangular outline and are intended to represent t? ediagrammatic arrangemeni shown for the corresponding elements and 3Similar recthe some significance the other tube grouns of circuit Awherein the some reference mime which are primed, lla e been used todesignate corresponding elemen The commutating ctor corresponding commto sun; ditions and are shown to 5 and the. other ctors are utilized ucearc-back conw d and claimed in U. S. letter granted August 9 f B. D.Bedfor othe assignee of the ent commutating reactor 35 compri cs threesaturable reacto elements 46,

5-"! and 48, each including a core meznber or winding 49 and controwindin The windings 49 are utilized to control t e r l of change ofcurrent throi the associated valves near the end or" the conductingperiods, and the inductance of the windings 4:3 is controlled by thecontrol windings "T be noted that the series winding of reactor 2? iscnnected in series relation with contro 58 of reactor 46. The coremember of reactor :6 is controlled in accordance wit e current of thisphase of pelyphase system. ly this arrangement each reactor element eprior to and during the greater part of conducting period of itsassociated electric valve and oilers relatively small induc On the otherhand, control winding efiects a substantial increa the series windingnear or at the end of the conducting periods so that the rate of changeof current through the electric valve means is reduced below apredetermined value so that positive ions associated with the ion plasmawithin the electric valve are allowed a sufiicient time to diffusewithin the valve without establishing high voltage gradients con duciveto arc-backs. The current limiting reactors 36 and the othercorresponding current limiting reactors are provided to limit the faultcurrents during arc-back or a short circuit on the direct current loop3D.

Each tube of the several tube groups is furnished with an appropriateexcitation circuit. The are initiating means is indicated by the ignitorelement 55 in each tube which is arranged to control the point ofinitiation of the arc in the appropriate half cycle of the respectivetubes in. the proper order. The energizing circuit for the variousignitors may be any of the several types well known the art. I haveillustrated the tubes as being of the ignitrc-n type because this typeof tube has suitable characteristics for heavy power projects, althoughit will be evident that my invention is not limited to a particular typeof electronic tube. With tubes of the ignitor type a suitable excitationcircuit is of the type described and claimed in application Serial No.413,232, or A. H. Mittag, filed October l, 1941, and assigned to theassignee of this application. This circuit is of the so-callecl magnetictype and, as illustrated, comprises an auxiliary source of alternatingcurrent 52 connected to energize an excitation transformer 53 which isutilized to transmit unidirectional impulses of current of peaked waveform to the ignitor control members El and cause arc to be initiated inthese tubes alternately during interval of time displaced substantially180 electrical degrees. The ignitcrs 5! are connected through aninsulating transformer 554 having a primary winding 55, a core 55 and apair of sec ondary windings 5i and. 53. The insulating transformer isused to transform the ignitor peaks up to the high potenial level thetubes. Unidirectional conducting devices 59 and are connected in circuitwith the respective ignitors iii. The primary winding 55 is connected tobe energized from the source through a nonlinear reactance or firingreactor 52 and a shunt connected capacitance 62, which elements incombination cause a peak of voltage to be generated across transformer54. The firing circuit also includes a linear reactance 63 connectedbetween the capacitor 52 and transformer t3 and which serves to preventdischarge of the capacitance to the supply circuit upon saturation ofthe firing reactor 6!. This linear reactor also serves to limit thecurrent derived from the supply circuit at the time capacitance 62discharges through transformer Winding The circuit may also be providedwith an additional shunt connected compensating circuit comprisingcapacitance 64 connected in series with a linear reactor 85 across thesupply circuit to maintain the voltage applied to the firing capacitance62 substantially constant for a predetermined range of phasedisplacements of the voltage of the firing circuit with respect to thesupply circuit voltage. A phase shifting circuit, many satisfactorytypes of which are available in the art, is used for adjusting the pointof arc ignition of the respective valves. For purposes of simplicity, Ihave shown, as representative of a phase shift circuit, a saturablereactor as which is provided with a direct current saturating wind ing61 arranged to be energized from a direct voltage source 68 through anadjustable resistor 59. A similar arc ignition circuit is indicated forthe group of tubes associated with circuit 2 and a pair of tubes of thetube group 29 has been selected by way of example. The circuit comprisessimilar elements in the same circuit relationship as that shown for tubegroup 26 and includes a source of excitation l5, excitation transformerH, insulating firing transformer 12 with its primary I3 and twosecondary windings l4 and 15 which are connected to the ignitors 5i ofthe oppositely connected valves through contact rectifiers l6 and "ll.The primary winding 13 is energized from a firing capacitor 78 through afiri reactor '59. A current limiting reactor 80 and voltage compensatingshunt circuit capacitor 8! and. reactor 82 are connected and operate asthe corresponding elements 63, 6 1 and E5 of the rectifying circuit. Aphase shiftin means is indicated by the saturable reactor 83 in whichthe 11-0 winding thereof is energized from a direct current source 84through adjustable resistor 857 Since either end of the system isintended to be operated at will as a rectifier or inverter, it isdesirable to utilize a control electrode or grid in each tube todetermine the time of starting of conduction between anode and cathodeand also to reduce the deionization period at the end of conduction. Ihave indicated a control electrode or grid 86 in each tube and have alsoindicated diagrammatically a grid excitation circuit for each tube groupcomprising an excitation transformer 81 connected to be energized fromthe auxiliary source 52 or Til through a suitable phase shifting device88. The transformer 31 may be of the peaking type. The grids 86 areconnected through an insulating transformer 89 in order to transform thefiring peaks up to the higher potential of the tubes. A grid bias sourceis indicated by the bias battery fill. The particular type of gridexcitation circuit forms no part of my present invention and varioustypes known in the art may be used to carry out my invention; however,reference is made to a particularly suit able grid excitation circuitwhich been found to operate satisfactorily in this system. Such anexcitation circuit is described and claimed in an application Serial No.589,941, of B. 1). Bedford, filed concurrently herewith and. assigned tothe assignee of the present application. The phase shifters 36 and 83 ofthe ignitor circuits and the phase shifters 88 of the grid excitationcircuits are tied together as indicated by the dotted lines in order tocontrol the magnitude and direction of power flow between the circuits Iand 2.

It is to be understood that each of the tubes or tube groups will befurnished with suitable arc ignition and grid control circuits such ashave been indicated diagrammaticall for the single pair of tubes of therectifier element 26 and inverter element 25 of unit B, and that thesecircuits will be connected to the respective ignitors and grids asindicated in a manner to effect the proper sequence of firing of theseveral tubes, as is well understood by those skilled in the art.

The general operation of the system illustrated is substantially asfollows: It will be assumed for the moment that unit B is being operatedseparately. Disconnect switches 34, 37, 40 d3 would be closed andcircuit interrupters I5 and 23 would also be closed. Under the functionsassumed for the respective tube groups, tube groups 26 and 21 will bearranged to operate as rectifiers and tube groups 28 and 29 asinverters. In this event, circuit I is the supply circuit and circuit 2the receiving circuit so that power flow is from circuit 5 to circuit 2.Initially, the respective rectifier and inverter firing point areadjusted by phase shifters 83 and 58 so that the rectifier voltage isequal to the inverter counter direct current voltage. Current andtherefore power flows through the direct current loop as when anythingtends to raise the rectifier voltage above the inverter counter voltage.By varying the angle of phase excitation of either the rectifier or theinverter, the magnitude as well as the direction of power flow may bereadily controlled. In the initial setting the rectifier firing circuitsare retarded in phase, depending upon the magnitude of the supplyvoltage, and the inverter firing circuits are advanced in phase. [is thephase of the rectifier firing circuit is advanced, the power fiows fromthe circuit 5 to circuit and the phase of the rectifier firing circuitis thereafter controlled to maintain the desired load. firing circuitshould als a safe margin or deicnization ,ngle. When changing the pairsof tube groups from rectifier to inverter operation for reverse powerflow, the phase position or" the firing circuit voltage must be shiftedapproximately 159 electrical degrees. These functions be performed bythe phase shift means of the respective tube group which in this caseare diagrammatically represented by the phase shifters S3 and While Ihave shown a partc of my invention, 5. will be obvio to those s in theart that various changes and modifications may be made without departingfrom my invention and I, therefore, aim in the appended claims to coverall such changes and modification as fall within the true spirit scopeof my invention.

What I claim as new and desire to secure by Letters Patent oi the UnitedStates is:

1. In combination, a pair of alternating current circuits, a pluralityof electronic tube groups, means for interconnecting certain of saidplurality of electronic tube groups with one of said alternating currentcircuits, means for interconnecting the remainder of said piiuality ofelectronic tube groups with the other circuit of said pair ofalternating current circuits, and means including a loop circuit forconnecting the re spective tube groups in a series circuit arrangementin which the tube groups associated with on of said alternating currentcircuits are arranged alternately with tube groups associated with theother of said pair of alternating current circuits.

2. In combination, a pair of polyphase alternating current circuits, aplurality of electronic tube groups each connected for polyphase fullwave power conversion, transforming means for interconnecting one halfof said electronic tube groups with one of said alternating currentcircuits, a second transforming means {or inte connccting the other halfof said plurality of tube groups with th other circuit of said pair ofcircuits, and means including a loop circuit for connecting therespective tube groups in aseries cir cuit arrangement in which therespective tube groups associated with one of said alternating currentcircuits are arranged alternately with the respective tube groupsassociated with the other of said pair of alternating current circuits.

3. In combination, a pair of alternating current circuits, a pluralityof electronic tube groups, means for interconnecting one half of saidelectronic tube groups with one of said alternating current circuits ina manner to constitute a plurality of electronic rectifiers, means forinterconnecting the other half of said electronic tube group-s with theother of said pair of alternating current circuits in a manner toconstitute a plurality of electronic inverters, and means including adirect current loop circuit for connecting the respective rectifiers andinverters in series relation and arranged alternately in said loopcircuit.

4. In combination, a pair of alternating current circuits, a pluralityof electronic tube groups, transforming means having a secondary windingwith a neutral terminal for interconnecting one half of said electronictube groups with one of said alternating current circuits in a manner toconstitute a plurality of electronic rectifiers, transforming meanshaving a secondary winding with a neutral terminal for interconnectingthe other half of said electronic tube groups with the other of saidpair of alternating current circuits in a manner to constitute aplurality of electronic inverters, means including a direct current loopcircuit for connecting the respective rectifiers and invertersalternately in a series circuit arrangement, and means for grounding theneutral terminal of the secondary winding of one of said transformingmeans.

5. In combination, a pair of three phase alternating current circuits, aplurality of electronic tube groups, means for connecting one half ofsaid plurality of tube groups as full wave rectifiers for twelve phaseoperation and including transforming means connected to said rectifiertube groups and having delta and Y connected rimary windings connectedto one of said alternating current circuits and a pair of secondarywindings zigzagged for a phase displacement of seven and one-halfdegrees, means for connecting the other half of said plurality of tubegroups as full wave inverters for twelve phas operation and includingtransforming means connected to said inverter tube groups and havingdelta and Y connected primary windings connected to the other of saidalternating current circuits and a pair of secondary windings zigzaggedfor a phase displacement of seven and one-half degrees, and meansincluding a direct current loop circuit for connecting the directcurrent terminals of the respective rectifier and inverter tube groupsalternately in a series circuit arrangement.

6. In combination, a pair of three phase alternating current circuits,two units of a plurality of electronic tube groups, transforming meansfor connecting one half of said plurality of tube groups of one of saidunits as full wave rectifiers for twelve phase operation, transformingmeans for connecting the other half of said plurality of tube groups ofsaid one unit as full wave inverters for twelve phase operation,transforming means having a fifteen degree displacement relative to saidfirst mentioned transforming means for connecting one half of saidplurality of tube groups of the other of said units as full waverectifiers for twelve phase operation, transforming means having afifteen degree displace lent relative to said second mentionedtransforming means for connecting the remaining half of said pluralityof tube groups of the other of said units as full wave inverters fortwelve phase operation, and means for selectively connecting anddisconnecting said units for operation separately as a twelve phassystem or jointly as a twentyfour phase system.

7. In combination, a pair of three phase alternating current circuits,two units of a plurality of electronic tube groups, means for connectingone half of said plurality of tube groups of one of said units as fullwave rectifiers for twelve phase operation and including transformingmeans connected to said rectifier tube groups and having delta and Yconnected primary windings connected to one of said alternating currentcircuits and a pair of secondary windings zigzagged for a leading phasedisplacement of seven and one-half degrees, means for connecting theremaining half of said plurality of tube groups of the said one of saidunits as full wave inverters for twelve phase operation and includingtransforming means connected to said rectifier tube groups and having.delta and Y connected primary windings connected to the other of saidalternating current circuits and a pair of secondary windings zigzaggedfor a leading phase displacement of seven and one-half degrees, meansfor connecting one half of said plurality of tube groups of the other ofsaid units as full wave rectifiers for twelve phase operation andincludin transforming means connected to said second mentioned rectifiergroups and having delta and Y connected primary windings connected tosaid one of said alternating current circuits and a pair of secondarywindings zigzagged for a lagging phase displacement of seven andone-half degrees, means for connecting the remaining half of saidplurality of tube groups of the other of said units as full waveinverters for twelve phase operation and including transforming meansconnected to said second mentioned inverter groups and having delta andY connected primary windings connected to the other of said alternatingcurrent circuits and a pair of secondary windings zigzagged for alagging phase displacement of seven and onehalf degrees, means includinga direct current loop circuit associated with each of said units "forconnecting the respective rectifiers and inverters of each unitalternately in a series circuit arrangement, and means for selectivelyconnecting and disconnecting said units for operation 10 separately as atwelve phase system or jointly as a twenty-four phase system.

8. In combination, a pair of alternating current circuits, a pluralityof electronic tube groups, means for interconnecting certain of saidplurality of electronic tube groups with one of said alternating currentcircuits, means for interconnecting the remainder of said plurality ofelectronic tube groups with the other circuit of said pair ofalternating current circuits, means including a loop circuit forconnecting the respective tube groups in a series circuit arrangement inwhich tube groups associated with one of said alternating currentcircuits alternate with tube groups associated with the other of saidpair of alternating current circuits, and means for controlling theamount of power interchanged between said alternating current circuits.

9. In combination, a pair of alternating current circuits, a pluralityof electronic tube groups, transforming means for interconnecting onehalf of said plurality of tube groups with one of said alternatingcurrent circuits for operation as rectifiers, transforming means forinterconnecting the remainder of said plurality of electronic tubegroups with the other circuit of said pair of alternating currentcircuits for operation as inverters, means including a loop circuit forinterconnecting the direct current terminals of said electronic tubegroups in a series circuit arrangement in which tube groups associatedwith one of said alternating current circuits alternate with tube groupsassociated with the other of said pair of alternating current circuits,and excitation control means connected to the tubes of each tube groupfor selectively determining and controlling the direction and magnitudeof the power interchanged between said alternating current circuits.

AUGUST SCHMIDT, JR.

REFERENCES CITED UNITED STATES PATENTS Name Date Willis Sept. 3, 1935Number 2,0 13,454

